1. Field of the Invention
The present invention relates to a flash-fixing color toner for use in the development of an electrostatic latent image in electrophotography and the like and a process for producing the same. More particularly, the present invention is concerned with a flash-fixing color toner which comprises as an indispensable ingredient a near-infrared light absorber composed mainly of an aminium salt compound which allows the triboelectric property of a toner to be regulated, and a process for producing the same.
2. Description of the Related Art
Electrophotography known in the art includes a system described in U.S. Pat. No. 2,297,691 and the like. In this system, a photoconductor (a photoconductive drum or the like) is generally used, an even electrostatic charge is provided on the surface of the photoconductor by corona discharge or the like, and an optical image is applied onto the photoconductor by various means to form an electrostatic latent image that is then developed with a fine powder called a "toner".
If necessary, the toner image is transferred onto a recording medium, such as paper. The toner image is then melted by means of pressing, heating, solvent vapor, light or the like to fix the toner image to the recording medium, thereby providing a print.
Particles formed by pulverizing a dispersion comprising a binder resin comprised of a naturally occurring or synthetic polymeric material and, dispersed in the binder resin, a coloring material and optionally additives, such as a charge control agent, to a size of about 1 to 30 .mu.m have hitherto been used as the toner for developing the electrostatic latent image.
In an electrophotographic two-component development process, the above-described toner is usually mixed with a carrying material (a carrier) including a ferromagnetic material, such as an iron powder, or a glass bead, before use in the development of the electrostatic latent image. In the case of a magnetic brush development process using as the carrier ferromagnetic particles, such as an iron powder or ferrite, the development is effected by mixing and stirring a developer comprising a toner and a carrier in a developing unit to effect triboelectrification, holding the triboelectrified toner with a magnetic roll in the developing unit to form a magnetic brush that is then transferred to a latent image portion on a photoconductor where charged toner particles alone are adhered to the latent image by electric attraction.
In this case, a polymer resin generally called an "oligomer", having a low molecular weight to exhibit a low melting viscosity, is extensively used as the binder resin, because the binder resin constituting the toner should be rapidly fused and exhibit a good fixation in the stage of the fixing of the toner to a recording medium.
In the above-described fixation, the toner on recording paper is fused by means of pressing, heating, exposing solvent vapor, irradiating light, etc. and then anchored to the recording paper. Among these fixing methods, the photo-fixing method has attracted attention because it has the following features.
(1) No deterioration of the resolution of the image in the stage of the fixing occurs by virtue of non-contact fixation.
(2) Quick start is possible because there is no need for waiting time after turning on the power.
(3) Even though a system failure may give rise to a recording paper jam within a fixing unit, there is no danger of the recording paper being ignited.
(4) The fixing can be successfully effected independently of the material and thickness of the recording paper even when use is made of glued paper (tack paper), preprint paper and various kinds of paper different from each other in the thickness.
The current most common photo-fixing method is a flash fixing method using a xenon flash lamp as a light source.
In a photo-fixing method that uses a light source having a high luminous intensity at wavelengths in an infrared region, such as the xenon flash fixing method, the addition of an infrared light absorber, such as an aminium salt compound, in a toner has been proposed in Japanese Unexamined Patent (Kokai) No. 61-132959 for the purpose of improving the light absorption capability of the toner and expanding the range of utilization of the photo-fixing method having the above-described advantages.
Many of compounds having a high infrared absorption capability have hues ranging from brown to black. The aminium salt compounds, however, exhibit an excellent infrared absorption capability and, at the same time, have a light color tone in a visible light region, so that the toner, as such, is less likely to have an influence on the color tone of the toner, which renders these compounds very useful for making up for the light absorption capability of the color toner.
Since, however, the aminium salt compounds are substances having a salt structure having a counter ion as represented by the following formulae: ##STR1## wherein X.sup.- is an arbitrary anion with an arbitrary valency; and ##STR2## wherein X.sup.- is an arbitrary anion with an arbitrary valency, when a high polar site (for example, a substance which have a tertiary amine group, such as dimethylaminoethyl methacrylate) and a high reactive ionic compound (for example, a quaternary ammonium salt) are present in the toner, the counter ions of the aminium salt compounds are extracted by the polar group or give rise to a counter ion exchange reaction with the ionic compound.
This causes a structural change of the aminium salt compound, which results in a shift in the light absorption band of the aminium salt compound and, in extreme cases, a complete loss of the capability of absorbing light having wavelengths in a flash light region.
On the other hand, the quaternary ammonium salt has an excellent charge control capability as a colorless positive charge control agent and is commonly used in color toners. The addition of an amine compound other than the quaternary ammonium salt to the toner, the introduction of an amine functional group into the binder resin, or other means, is used as a method for imparting a positive chargeability to the toner without use of the quaternary ammonium salt. As described above, however, the amine compound too has a high possibility of causing a structural change to the aminium salt compound.
For the reasons set out above, the aminium salt compound for improving the light absorption capability cannot be used in combination with the amine compound for imparting a charge control capability (hereinafter referred to as a "charge control agent"), such as a quaternary ammonium salt, and there is a problem that a positive charge color toner having an excellent light absorption capability and a good photo-fixability is poor in the chargeability, while the positive charge color toner having an excellent chargeability is poor in photo-fixability.
The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a flash fixing toner that enables the structural change of the aminium salt compound to be minimized while the aminium salt compound and a charge control agent coexist in a toner, thereby attaining a combination of an excellent flash fixability with an excellent chargeability, and a process for producing the same.